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Products of two palindromic primes.
6

%I #28 Jan 11 2022 21:50:01

%S 4,6,9,10,14,15,21,22,25,33,35,49,55,77,121,202,262,302,303,362,382,

%T 393,453,505,543,573,626,655,706,707,746,755,766,905,917,939,955,1057,

%U 1059,1111,1119,1149,1267,1337,1441,1454,1514,1565,1574,1594,1661,1765,1838,1858

%N Products of two palindromic primes.

%C Intersection of A001358 and A033620; A046368 is a subsequence. - _Reinhard Zumkeller_, Apr 10 2011

%C Equivalently, semiprimes where both prime factors are palindromes. - _Franklin T. Adams-Watters_, Apr 11 2011

%C See A046376 for the subsequence of palindromic terms. - _M. F. Hasler_, Jan 04 2022

%H Reinhard Zumkeller, <a href="/A046368/b046368.txt">Table of n, a(n) for n = 1..1000</a>

%t palQ[n_] := Reverse[x = IntegerDigits[n]] == x; Select[Range[1800], PrimeOmega[#] == 2 && And @@ palQ /@ First /@ FactorInteger[#] &] (* _Jayanta Basu_, Jun 23 2013 *)

%o (PARI) select( {is_A046368(n)=bigomega(n)==2 && vecmin( apply( is_A002113, factor(n)[, 1]))}, [1..9999]) \\ _M. F. Hasler_, Jan 04 2022

%Y Cf. A001358 (semiprimes), A002113 (palindromes), A002385 (palindromic primes), A046376 (subsequence of palindromes), A046400.

%K nonn,base

%O 1,1

%A _Patrick De Geest_, Jun 15 1998

%E Definition clarified by _Franklin T. Adams-Watters_, Apr 11 2011

%E Definition simplified by _M. F. Hasler_, Jan 04 2022